The present invention broadly relates to the exploitation of tidal flow for the purpose of extracting energy therefrom, and, more specifically, concerns a new and improved construction of a tidal power plant and a method of operating the same.
Tidal power plants serving the purpose of extracting energy from tidal flow commonly employ at least one water turbine arranged between the sea and a storage reservoir separated therefrom.
Tidal power plants or installations have already been proposed, in which a storage reservoir is separated from the sea by a wall or a dam. In the presence of a rising tide, the water is conducted from the sea via a water turbine and/or openings in the wall or dam into the storage reservoir. On the other hand, when the tide falls this flow path is closed by flaps or sliders and there is opened a path in the opposite direction from the storage reservoir to the sea by means of the turbine. In this way, the turbine is traversed in the same direction during both tidal flow phases and generates energy during both such phases. This design concept proceeded from the notion that to extract as much energy as possible, both tidal flow phases or flow directions must be exploited if possible.
Tidal power plants utilizing the above concept are described, for example, in German Pat. No. 98,894, granted Jan. 23, 1897 or French Pat. No. 1,075,360, granted Apr. 14, 1954. The water turbine is preferably arranged in the dam or barrier wall so as to have a vertically extending axis. This water turbine has an inlet and an outlet in each case both on the sea side and the reservoir side. In rhythm with the tides, alternately in each case an inlet on the one side and an outlet on the other side is opened or closed by slideable flood gates or dam panels. When both inlets of the turbine are closed at the same time, a free through-flow between the sea and the reservoir is available beneath the turbine.
A disadvantage with such state-of-the-art tidal power plants is that the extraction of energy only takes place in tidal phases, in which a quick change of the sea level occurs; i.e., preferably between the maximum and minimum water level. At most times, however, the level difference which determines the efficiency of the turbine, is only relatively small, and the times which can be exploited for extracting energy with a practical efficiency are only short. In addition, it is a disadvantage that on both sides of the turbine shutoff devices are necessary which are operable under pressure, and these are therefore costly and expensive. Furthermore, the arrangement of the turbine with vertical axis and with an electric generator mounted on this axis over the turbine, necessitates a considerable overall height of the power plant as a whole, and the through-flow channel lying beneath the turbine requires an additional depth. The cost of construction and the costs of such previously known power plants were therefore considerable, apart from the generally less than optimum performance and the susceptibility to breakdown brought about by the complexity of the installation.
In U.S. Pat. No. 4,261,171, granted Apr. 14, 1981 and U.S. Pat. No. 4,279,539, granted July 21, 1981, a tidal power plant is described using a tube or Kaplan turbine with a horizontal axis and arranged in one through-flow channel between the sea and the storage reservoir. In order to make possible an extraction of energy both on rising and on falling tide cycles, with the same direction of through-flow of the turbine, the turbine is constructed so as to rotate through 180.degree.. To obtain a free flow from the sea into the reservoir or vice-versa, the turbine is constructed so as to slide in vertical or horizontal direction, so that upon such displacement the through-flow channel is freed. Again, such power plant design is very expensive and requires complex mechanisms for the rotation and displacement of the turbine.